The present invention relates to a low pressure gas-discharge switch containing at least two main electrodes. These main electrodes are disposed at a distance d from each other in an arcing chamber and constitute one cathode and one anode of a discharge gap for the low-pressure gas discharge. The low-pressure gas discharge is ignited by increasing the electron density in the rear cathode space. The arching chamber contains an ionizable gas filling having a pressure p which is selected so as to allow the igniting voltage of the low-pressure gas discharge to diminish as the product p.times.d (i.e, pressure x distance) increases.
The usual graphic representation of the gas-discharge gap's control characteristic, the igniting voltage in dependence upon the product of the gas pressure p and the electrode spacing (i.e., anode-to-cathode distance) d, constitutes an important aid for characterizing electric discharge units when the firing probability considered. When the dielectric strength of a given gas-discharge gap is determined, generally the infinitely larger plate-type capacitor and its control characteristic are drawn upon for comparison. However, the practical specific embodiment of such discharge gaps has electrodes with finite dimensions. While determining the right hand branch of the ignition characteristic (Paschen curve) inclusive of the voltage minimum, merely arranging two flat, rounded-off plates, possibly provided at the edges with a so-called Rogowski profile, parallel to one another is sufficient. However, such an arrangement is useless for analyzing control characteristics in the left part of the Paschen curve, since indirect (i.e., diverted) discharges can occur then.
Such indirect or diverted discharges can be avoided by using an electrode construction with plate electrodes disposed coaxially to one another, bent away from one another at their edges with a radius of curvature that is small relative to the electrode spacing, and supported along the inner cylindrical insulator surface. Thus, a gap is always formed between the bent, cylindrical edge area of the electrodes and the inner wall of the hollow-cylindrical insulator. This specific embodiment of a low-pressure gas-discharge gap enables the control characteristic to be determined, for example, for different inert and molecular gases in the near-strike range as well (i.e., left of the minimum of the Paschen curve) (see Proc. VIIth Int. Conf. Phenom. in Ionized Gases, Beograd 1965, vol. 1, pp. 316-326).
Gas-discharge switches controlled by a pulsed low-pressure gas discharge are also known. They operate currents of 10 kA, for example, at a voltage of 20 kV. Such a discharge switch contains an anode and a cathode, each being provided with coaxial openings. Each are separated from one another at the edge by a ring-shaped insulator. A controlling device is provided for the gas discharge. It contains an electrode with a cage-like construction often described as a hollow electrode. The hollow electrode is connected in an electrically conductive manner to the cathode and is thus connected to the cathode potential. It encircles the rear cathode space and separates it from an area of a pre-ionization. The gas discharge between the cathode and the anode is fired by injecting charge carries. The discharge gap is ignited in two steps: first a pre-ionization is produced by an auxiliary electrode through a glow discharge. Subsequently, a trigger electrode receives a negative firing pulse, and the entry of charge carries into the cage-type electrode is permitted because the potential of a blocking electrode is set to zero. The discharge is introduced with the entry of the charge carriers into the cage-type electrode (see J. Phys. E: Sci. Instr. 19 (1986), The Inst. of Physics, great Britain, pp. 466-470 or Japanese Journal of Applied Physics 29 (1990) February, no. 2, part 2, Tokyo, JP, pp. L 371-374).